Steel reinforcing rods embedded in concrete structures corrode in reaction with chlorides present in concrete. Electrically connecting a zinc anode to the reinforcing steel and placing the zinc anode in a position where the flow of ions is permitted through the surrounding concrete structure serves as an effective means of preventing such corrosion.
When concrete deteriorates and/or becomes spalled, shuttering and forms are used to contain wet cement used to repair the concrete. These forms are temporary and have no anodic function. A jacketing system as described in U.S. Pat. No. 5,714,045 has been used which is permanent, has an anode and works in wet zone areas. The jacketing system, however, may not perform optimally in dry zone areas or those that might become dry at some time.
This disclosure describes a method of making a dry prefabricated panel containing a zinc anode plus a solid electrolyte which works in wet and dry zone areas, a method of attaching such a prefabricated composite panel to concrete structures, a method to use the panel as a shuttering or form for molding and forming concrete or mortar used to fill and repair spalled areas and panel constructions formed by such methods.
In one embodiment, solid electrolytic mortar or cement, which is preformed by a liquid spraying method, produces a laminated or layered panel for use as a sacrificial galvanic anode. A zinc anode plus one more electrically conductive anode connecting wires are embedded, sandwiched or laminated within the solid electrolyte. The panel maintains galvanic activity under low humidity conditions and quickly and easily reactivates from a dry state when re-hydrated.
Panels according to this disclosure can be made by spraying a liquid mixture of ingredients which later set to form a solid electrolyte mixture serving as a galvanic cement. The solid electrolyte mixture is uniquely different from conventional cements in that when set, the pH of the mixture is between 10.5 and 11.0. This relatively low pH facilitates the use of conventional glass fiber reinforcement without degradation of the glass fibers.
Conventional glass fibers cannot be used in conventional Portland cement mixes, as these mixes have a pH of about 12.5. This relatively high alkaline pH corrodes the surface of the glass fibers and leads to weakening of the cement composite. Special high alkaline resistant glass fibers can be used but these are much more expensive than conventional glass fibers. Moreover, conventional glass fibers cannot be used in any conductive galvanic cements which have a pH of 12.5 or higher without risk of fiber degradation and weakening of the composite. Again, special high alkaline resistance glass fibers can be used, but these are much more expensive.
In another embodiment, a glass fiber reinforcing technique produces a finished product in the form of a panel which is strong enough to serve as a functional structural member which can retain, shape and form wet cement during the repair of concrete structures.
A multi-component solid electrolyte panel system developed for use in dry zone cathodic protection of reinforced concrete structures includes a zinc anode, such as in the form of a wire mesh, expanded metal, a knitted or woven grid, a perforated sheet or any other suitable form preferably an open form. Openings or gaps in the zinc anode material allow for physical reinforcement of the panel throughout its entire thickness as the mortar flows through the spaces or openings in the zinc anode material. Large flat galvanic panels mounted onto planar reinforced concrete surfaces suffer from a degree of shielding of the anode surface facing away from the structure. Openings in the anode therefore also facilitate electrical galvanic activity on the side of the anode facing away from the reinforced concrete structure and improve the overall galvanic performance of the anode. The panel can be further strengthened by the addition of staple glass fibers to the panel mortar or cement in a manner similar to glass reinforced plastic materials. Quartz sand can also be used as an optional void filler and reinforcing filler.
In another embodiment, the solid electrolyte mortar which forms the panel matrix is made by mixing two liquid mortar components to which fillers are then separately added. This mixture reacts and hardens over a 24 hour period. To fabricate a panel according to this disclosure, the liquid mortar components of the solid electrolyte system are premixed and adjusted with an addition of water to provide a viscosity suitable for pumping or spray application. This mixture is pumped or sprayed to form a stream into which can be entrained any combination of or all of the following components: sand or similar particulate mineral filler; a lenticular reinforcing mineral filler such as Wollastonite; natural mineral fibers similar to Asbestos; synthetic organic fibers such as polyester; and synthetic inorganic fibers such a glass staple fibers. The fillers can be introduced directly into the flowing mortar stream or introduced into a separate stream which is combined with the mortar stream.
The two separate streams of wet mortar and dry filler components combine into a composite mixture and the combined streams form a spray which is sprayed and deposited onto a carrier panel or mold selected from a material which will release the composite when it has dried. A steel or aluminum platen can be used for this purpose, as can a plastic or wood platen. The platen can be coated with a conventional lubricant or release agent prior to application of the stream of wet composite material. The platens can be oversized to allow for the production of oversized anode panels, which when dried and solidified, can be cut or trimmed to a final desired shape and size.
Once a suitable initial thickness of composite mortar material has been sprayed or otherwise deposited onto a carrier panel or shaped mold, the wet composite mixture can be consolidated by the use of a multiple disc roller to compress the composite mortar material and remove trapped air pockets. When the wet composite mortar material is free of air, a zinc anode is positioned in place on top of the wet composite mortar material deposited on the platen. Further spraying of the liquid and filler components resumes to embed the zinc anode within the wet composite mortar material and build the final thickness of the panel.
The thickness of the sprayed electrolyte/particulate filler/fiber mortar mixture applied before and after placing and/or laminating the zinc anode on a platen can be varied so as to place the anode centrally or biased towards either finished panel surface. The relative proportions of electrolyte, particulate filler and fiber reinforcement can also be varied to modify the physical properties of the finished product. The panel is finished by connecting a wire to the zinc anode which can be formed as a mesh, grid or perforated metal anode.
The finished panel has the potential to be used in the repair of planar and three dimensional concrete structures. Significant advantages of the panel include the prefabrication of electrolytic anode materials which reduces expensive “on the job” work. The panel is strong enough to act as a “leave in place” shuttering, mold, or formwork for concrete repair. The unique construction technique allows for the prefabrication of simple or intricate two and three dimensional forms, such as forms to fit the external surface of cylindrical concrete columns, pilings or the complex junctions of two or more support piles, for example. Moreover, there is sufficient compliance in the finished anode panel to bend to accommodate surface irregularities or “out of round” piles.
A particular advantage of preforming a glass fiber reinforced anode panel prior to application in the field is the ability to use a thinner layer of concrete or mortar than that used in applications where the anode panel is applied in the field with liquid concrete. When applied in the field, liquid concrete requires significant time to set and solidify. In the case of the subject preformed fiber-reinforced anode panel, a mold can be formed in the shape of the component or object or application to which the anode is to be applied such that a glass fiber reinforced anode is preformed on a platen or mold, taken in solid form to the field, and applied directly in the field without the requirement of concrete pouring and setting. This is an advantage over prior techniques that had to be assembled in the field where forming proper concrete joints was quite difficult and often required expensive rework where the poured concrete did not form a proper seal or joint around the object to which the anode was applied.
It can be appreciated that field labor and construction costs are significantly reduced and significant time savings are achieved with the subject glass fiber reinforced anode. In addition, greater quality control in the fabrication of the subject glass fiber reinforced anode can be achieved in the factory than in the field.
In the case of flat surfaces to which the glass fiber anode panel is applied, preformed sheets of flat panel may be fabricated, taken to the field, and simply cut to shape in those cases where planar surfaces are to be protected by application of a glass fiber reinforced anode panel. Large cylindrical concrete piles can be covered with two or more arcuate panels formed on arcuate molds. These panels, which can be formed as segments of a cylinder, can be applied in the field as sections to form a sleeve around a concrete piling or other cylindrical support. Flat panels can be easily applied to flat concrete surfaces in the field.
It should be noted that glass fibers prevent the breaking of the solid mortar electrolyte and allow the electrolyte to be formed without adhesives. In this manner, instead of the electrolyte mortar forming an adhesive bond with the underlining substrate to which the anode is applied, the glass fiber reinforced anode panel can be applied in the field with a separate adhesive. While microcracks may occur in the solid electrolyte panel, the glass fibers prevent any one crack from propagating to the point where the panel actually breaks.
Fibrous reinforcing materials, such as the glass fibers noted above, can be used alone or with particulate filler materials added to the fiber spray stream. The filler material can be of conventional particle shape (roughly irregular spheres), platelet shaped. The reinforcing material can also be chosen with advantage from synthetic or natural fillers which have lenticular or needle-like configurations—such as natural Wollastonite, which is a calcium silicate. These elongated pigment particles have an aspect ratio (ratio of length to width/thickness). Particles having a higher aspect ratio have a noticeable effect in increasing the strength of the final solidified form of the galvanic cement used as a matrix for the panel.
The filler material added to the electrolytic mortar can be a natural expanded material like vermiculite or pearlite or a synthetic product such as polystyrene or various forms of ground plastic foam. In use, the zinc anode corrodes within the panel. This corrosion creates oxides and other corrosion products that occupy more space that the initial volume of the zinc metal which created them. The use of expanded or spongy materials as fillers allows for these fillers to be crushed within the panel to yield extra space for the oxidation products of the Zinc anode which would otherwise exert disruptive and destructive stress on the anode panel itself or create stress within the galvanic cement that holds the panel onto a substrate. The use of ground plastic foam or other void formers creates air pockets which satisfy the expansion needs of the zinc corrosion products. The filler material can also include short staple fibers like glass.
As noted above, a spray-formed galvanic anode panel is produced by spraying a mixture of liquid stage conductive cement (hereafter referred to as “liquid”), glass fibers and optional filler material around a zinc anode. The liquid can be sprayed from a conventional pneumatic spray gun, a high-volume low-pressure spray gun, an airless pressure spray gun or combinations of these spray guns. The sprayed liquid is directed towards a collector mold or pattern.
The glass fibers are introduced into an air stream and conveyed towards a collector mold. The sprayed liquid stream and the air stream containing entrained glass fibers meet at the surface of the collector mold or ideally mix in a combined airstream before meeting the collector mold. A deposit of liquid coated glass fibers is collected on the surface of a mold which can be planar or three dimensional in form.
At some stage after a certain thickness of liquid coated fibers has built up on the collector mold, a zinc anode is laid onto the wet mortar and composite deposited on the collector mold surface. The zinc anode is ideally in an expanded, perforated, mesh or other open form and is formed to fit and conform to the surface of the liquid-coated fibers on the surface of the collector mold. Once the zinc anode is in place, the deposition of liquid coated fibers continues and adds a further coating of liquid coated fibers onto the exposed surface of the zinc anode. This additional application of mortar and glass fibers (liquid) serves to incorporate and laminate or embed the zinc anode within the mass of liquid coated fibers.
The deposit of liquid coated fibers and integral zinc anode on the collector mold is preferably consolidated before the liquid hardens. Adjustments of the amount of liquid coated fibers before and after adding the zinc anode to the panel assembly allows for any thickness of reinforced anode panel on either side of the zinc anode. Thus, an asymmetric placement of the zinc anode within the final cured panel can be achieved, with the ability to present the anode closer to the surface of the reinforced concrete which contains the reinforcing steel or rebar which need to be protected. This allows for a shorter galvanic path, less impeded by the glass (or other) fiber panel reinforcements or fillers.
It is also possible by modifying the ratio of liquid to fiber sprayed at various stages of the production of a panel to achieve a panel surface rich with a greater concentration of the galvanically active conductive electrolyte mortar material on the side of the panel presented to the concrete surface than on its other (exterior) side. This reduces any interference to the flow of protective ionic current that may be presented by the fiber reinforcement on the side of the panel presented to the concrete surface containing the steel to be protected. The thinner internal (concrete side) section will have lower strength as will an inner section made with a liquid rich construction. The overall strength of the panel can be restored by a thicker external panel section which is thicker and/or contains a higher percentage of reinforcing glass fibers. These two processes can be arranged to be seamless so no distinct layers are produced.
Formed anode panels of any construction described herein can be fixed to a reinforced concrete surface to be galvanically protected by cementing a galvanic anode panel to the concrete with fresh conductive electrolyte adhesive, or cementing the panel to the concrete with cement adhesive material, or using either of these two methods augmented by optional concrete screws or other types of mechanical anchors which can be left in place after the cement or mortar has set or removed. These mechanical anchors attach the panels to uncompromised areas of the underlying concrete.
Attaching the galvanic panels to damaged reinforced concrete can be arranged such that the prefabricated galvanic anode panels cover spalled and damaged areas of the concrete. Such covered areas can then be filled with conventional liquid concrete or galvanic adhesive with the galvanic panels acting as “leave in place” shuttering. The concrete or galvanic adhesive filling can be achieved for example by drilling a series of holes in the galvanic panel and injecting concrete or galvanic adhesive mix though these holes. These holes can be plugged after injection.
Formed galvanic anode panels can be fixed to a concrete surface to be protected “dry”—that is without any conventional or galvanic adhesive. These panels can be fixed by conventional concrete anchors and may be arranged such that a cavity exists behind the entire panel. These panels can be arranged such that they butt together and seal over the surface of the concrete to be protected. Alternatively, these panels can be fitted with a perimeter seal which defines a cavity behind the panel. Seals can be in the form of a blade or flexible barrier seal or a compressible seal, or formed by a liquid adhesive, for example a construction adhesive, which sets and seals the edges of the panels prior to cavity filling.
Once sealed, the cavities behind the galvanic panels are filled by injection with conductive galvanic adhesive or a cement mix which sets and provides a galvanic path for the protective galvanic current as well as adding additional anchoring for the galvanic panel. Freshly applied concrete within the cavity behind the galvanic anode panel can have a low ionic conductivity when fresh, which can impede substantial immediate galvanic protection of the reinforcing steel. This changes with time as chlorides from the existing concrete permeate through the fresh concrete and regular galvanic protection is established. To prevent or offset this impediment to initial galvanic protection, the cavity defined by the panel can be filled with an adhesive which can be adjusted to provide enhanced immediate and long term galvanic protection of the underlying steel reinforcement. The cavity can also be filled with a conventional concrete dosed with electrolytes to provide enhanced ionic conduction for immediate galvanic protection of the underlying steel.
Finished panels can include external coatings applied before or after the panels are affixed to a concrete structure. These coatings can be cementitious or polymeric, impervious or permeable. Such exterior coatings can be tailored to control the conditions within the reinforced concrete structure which is being protected and can be arranged to improve the abrasion or external damage resistance of the panel.
Examples of successfully applied organic polymeric coatings are Epoxy and polyurea. Examples of cementitious coatings are Portland cement based mixtures with fine mineral fillers. These cementitious coatings can be dosed with organic emulsion polymers to control ultimate permeability of the final coating.
In the various views of the drawings, like reference numerals designate like or similar components.